Global positioning system (GPS) apparatuses rely on a space-based global navigation satellite system (GNSS). GNSS satellite vehicles (SV) broadcast signals from space. GPS receivers use the SV signals to calculate three dimensional (3D) locations (e.g., latitude, longitude, altitude) and/or the current time.
A GPS has three basic components—absolute location, relative movement, and time transfer. A GPS receiver calculates its position by precisely timing the signals sent by GNSS satellites. The GNSS satellites send signals that include the time the message was sent, precise orbital information (the ephemeris), and general system health with rough orbits of the GNSS satellites (the almanac). Receivers use the messages received to determine the message transit times and thus to compute the distance to satellites.
GNSS SVs continuously broadcast a navigation message at a rate of 50 bits/second. A complete message is composed of 25 full frames. Each frame is 30 seconds arranged as distinct groupings of 1,500 bits of information. Frames can then be further subdivided into 5 subframes of length 6 seconds and with 300 bits each. Thirty second frames begin precisely on the minute or half minute as indicated by the atomic clock on the satellite. Since conventional satellites continuously broadcast, conventional receivers typically continuously receive and continuously update solutions.